This invention relates generally to an improved means for feeding parts such as electronic components, by vibration, to an unload station of a vibratory feeder, and picking up the components by an unloader for a subsequent operation.
An example of such an apparatus is disclosed in U.S. Pat. No. 4,151,945 directed to placement of electronic components on a fluxed hybrid circuit substrate. In accordance with an automated program, the apparatus picks up individual components at a supply station such as a vibratory feeder by a vacuum pick-up head and translates these components to another location for population of a printed circuit board. In this patent, the pick-up head is used to orient and center each component, after selection and prior to placement. Although the apparatus of U.S. Pat. No. 4,151,945 provides means for orienting and centering each chip after selection and prior to placement, numerous other pick-up devices of this general nature do not provide means for orienting and centering the component; they rely upon the positioning of the component at the supply means prior to pick-up.
Numerous vibratory feeder bowls and vibratory linear feeder track devices have been used in an attempt to precisely position each chip, in turn, for pick-up by an unloader head. Examples of vibratory linear feeders are: U.S. Pat. No. 4,282,965, FEEDING AND ORIENTING DEVICE, Bates, et al. issued Aug. 11, 1981, and U.S. Pat. No. 4,282,966, FEEDING AND ORIENTING DEVICE, Bates, et al., issued Aug. 11, 1981.
Prior art vibratory feeders have provided a stop means which is integral with the feeder in order to stop the leading component in a position for pick-up by the unloader. Various problems have been encountered with this type of structure. For instance, when a component has reached the unload station and abuts the stop means, prior to pick-up, the stop means acts like a little hammer beating on the end of the part at an amplitude of vibration depending upon the setting of the feeder vibrator motor and the number of parts in the feeder. This constant, although small, vibration of a component against the stop means while at the unload station can cause inaccuracies in the pick-up of very small components and is detrimental to population of the printed circuit board. Further, since the feeder bed (usually supported on spring-metal strips) and the mass in the feeder changes each time one of the components is removed, the vibration amplitude changes. Stated another way, the amplitude of vibration changes as the number of parts in the feeder changes. Because of this dynamic change in vibration, it is difficult to compensate for the variable movement of the component (due to the "hammer" effect) that is engaging the stop in the unload station. This dyanamic change in vibration also requires the operator to constantly change the vibration motor setting as a means of compensation for the "hammer" effect. With a large number of parts in the feeder, it is necessary to reduce the amplitude of vibrations to obtain the necessary accuracy of pick-up, resulting in a subsequent loss of feed rate to the unload station. With a lesser number of parts in the feeder, a greater amplitude of vibration is required in order to keep the subsequent components fed up against the first component that is at the unload station; resulting in a "jittering", less smooth feed of components.
When dealing with very small components, such as miniature capacitors having no leads, the accuracy of positioning of the pick-up head with respect to the component that is at the unload station is critical for subsequent precise population of the printed circuit board.